Ambient temperatures in wide regions of the world are close to or below the freezing point of water. Freezing is lethal to most higher organisms, and poses a severe threat to the survival of organisms such a fish, plants and insects inhabiting polar and subpolar environments. In response, many organisms have developed mechanisms that protect them from freezing or its negative consequences. One of these mechanisms is the production of antifreeze proteins, whose specific function is the suppression of the freezing point and the modification or inhibition of ice-crystal growth. Several structurally very diverse antifreeze proteins have been identified. Despite their sequence and structural diversity they all function similarly through a direct crystal adsorption and kinetic growth inhibition. Analogous protein crystal interactions are widespread through nature in bio-mineralization processes. Our project aims are to characterize the nature of these unique proteins, to identify critical structural and dynamic properties, and to study the protein interactions with water and ice. The desired understanding of the AFP mechanism of action will facilitate the engineering of antifreeze compounds with defined properties for the efficient use in cryogenic storage of cells, blood and organs, and for conferring freezing resistance to crop and food. The aims of this proposal focus on two representative types of fish antifreeze proteins. Specifically, 1) the dynamic properties of Type III AFP will be characterized by NMR spectroscopy relaxation experiments at ambient and physiological temperatures.2) the ice-binding surfaces of three Type I AFP isoforms will be localized and characterized in systematic structure-function studies.3) the AFP-water interactions will be characterized by NMR spectroscopy, and methods will be developed to study the protein in supercooled solution and upon binding to ice.